/* $OpenBSD: dh.c,v 1.76 2026/02/08 19:54:31 dtucker Exp $ */

/*

 * Copyright (c) 2000 Niels Provos.  All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

#include "includes.h"

#ifdef WITH_OPENSSL

#include "openbsd-compat/openssl-compat.h"

#include <errno.h>

#include <stdarg.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <limits.h>

#include <openssl/bn.h>

#include <openssl/dh.h>

#include "dh.h"

#include "pathnames.h"

#include "log.h"

#include "misc.h"

#include "ssherr.h"

static const char *moduli_filename;

void dh_set_moduli_file(const char *filename)

{

  moduli_filename = filename;

}

static const char * get_moduli_filename(void)

{

  return moduli_filename ? moduli_filename : _PATH_DH_MODULI;

}

static int

parse_prime(int linenum, char *line, struct dhgroup *dhg)

{

  char *cp, *arg;

  char *strsize, *gen, *prime;

  const char *errstr = NULL;

  long long n;

  dhg->p = dhg->g = NULL;

  cp = line;

  if ((arg = strdelim(&cp)) == NULL)

    return 0;

  /* Ignore leading whitespace */

  if (*arg == '\0')

    arg = strdelim(&cp);

  if (!arg || !*arg || *arg == '#')

    return 0;

  /* time */

  if (cp == NULL || *arg == '\0')

    goto truncated;

  arg = strsep(&cp, " "); /* type */

  if (cp == NULL || *arg == '\0')

    goto truncated;

  /* Ensure this is a safe prime */

  n = strtonum(arg, 0, 5, &errstr);

  if (errstr != NULL || n != MODULI_TYPE_SAFE) {

    error("moduli:%d: type is not %d", linenum, MODULI_TYPE_SAFE);

    goto fail;

  }

  arg = strsep(&cp, " "); /* tests */

  if (cp == NULL || *arg == '\0')

    goto truncated;

  /* Ensure prime has been tested and is not composite */

  n = strtonum(arg, 0, 0x1f, &errstr);

  if (errstr != NULL ||

      (n & MODULI_TESTS_COMPOSITE) || !(n & ~MODULI_TESTS_COMPOSITE)) {

    error("moduli:%d: invalid moduli tests flag", linenum);

    goto fail;

  }

  arg = strsep(&cp, " "); /* tries */

  if (cp == NULL || *arg == '\0')

    goto truncated;

  n = strtonum(arg, 0, 1<<30, &errstr);

  if (errstr != NULL || n == 0) {

    error("moduli:%d: invalid primality trial count", linenum);

    goto fail;

  }

  strsize = strsep(&cp, " "); /* size */

  if (cp == NULL || *strsize == '\0' ||

      (dhg->size = (int)strtonum(strsize, 0, 64*1024, &errstr)) == 0 ||

      errstr) {

    error("moduli:%d: invalid prime length", linenum);

    goto fail;

  }

  /* The whole group is one bit larger */

  dhg->size++;

  gen = strsep(&cp, " "); /* gen */

  if (cp == NULL || *gen == '\0')

    goto truncated;

  prime = strsep(&cp, " "); /* prime */

  if (cp != NULL || *prime == '\0') {

 truncated:

    error("moduli:%d: truncated", linenum);

    goto fail;

  }

  if ((dhg->g = BN_new()) == NULL ||

      (dhg->p = BN_new()) == NULL) {

    error("parse_prime: BN_new failed");

    goto fail;

  }

  if (BN_hex2bn(&dhg->g, gen) == 0) {

    error("moduli:%d: could not parse generator value", linenum);

    goto fail;

  }

  if (BN_hex2bn(&dhg->p, prime) == 0) {

    error("moduli:%d: could not parse prime value", linenum);

    goto fail;

  }

  if (BN_num_bits(dhg->p) != dhg->size) {

    error("moduli:%d: prime has wrong size: actual %d listed %d",

        linenum, BN_num_bits(dhg->p), dhg->size - 1);

    goto fail;

  }

  if (BN_cmp(dhg->g, BN_value_one()) <= 0) {

    error("moduli:%d: generator is invalid", linenum);

    goto fail;

  }

  return 1;

 fail:

  BN_clear_free(dhg->g);

  BN_clear_free(dhg->p);

  dhg->g = dhg->p = NULL;

  return 0;

}

DH *

choose_dh(int min, int wantbits, int max)

{

  FILE *f;

  char *line = NULL;

  size_t linesize = 0;

  int best, bestcount, which, linenum;

  struct dhgroup dhg;

  if ((f = fopen(get_moduli_filename(), "r")) == NULL) {

    logit("WARNING: could not open %s (%s), using fixed modulus",

        get_moduli_filename(), strerror(errno));

    return (dh_new_group_fallback(max));

  }

  linenum = 0;

  best = bestcount = 0;

  while (getline(&line, &linesize, f) != -1) {

    linenum++;

    if (!parse_prime(linenum, line, &dhg))

      continue;

    BN_clear_free(dhg.g);

    BN_clear_free(dhg.p);

    if (dhg.size > max || dhg.size < min)

      continue;

    if ((dhg.size > wantbits && dhg.size < best) ||

        (dhg.size > best && best < wantbits)) {

      best = dhg.size;

      bestcount = 0;

    }

    if (dhg.size == best)

      bestcount++;

  }

  free(line);

  line = NULL;

  linesize = 0;

  rewind(f);

  if (bestcount == 0) {

    fclose(f);

    logit("WARNING: no suitable primes (size %d/%d/%d) in %s",

        min, wantbits, max, get_moduli_filename());

    return NULL;

  }

  which = arc4random_uniform(bestcount);

  linenum = 0;

  bestcount = 0;

  while (getline(&line, &linesize, f) != -1) {

    linenum++;

    if (!parse_prime(linenum, line, &dhg))

      continue;

    if ((dhg.size > max || dhg.size < min) ||

        dhg.size != best ||

        bestcount++ != which) {

      BN_clear_free(dhg.g);

      BN_clear_free(dhg.p);

      continue;

    }

    break;

  }

  free(line);

  line = NULL;

  fclose(f);

  if (bestcount != which + 1) {

    logit("WARNING: selected prime disappeared in %s, giving up",

        get_moduli_filename());

    return (dh_new_group_fallback(max));

  }

  return (dh_new_group(dhg.g, dhg.p));

}

/* diffie-hellman-groupN-sha1 */

int

dh_pub_is_valid(const DH *dh, const BIGNUM *dh_pub)

{

  int i;

  int n = BN_num_bits(dh_pub);

  int bits_set = 0;

  BIGNUM *tmp;

  const BIGNUM *dh_p;

  DH_get0_pqg(dh, &dh_p, NULL, NULL);

  if (BN_is_negative(dh_pub)) {

    logit("invalid public DH value: negative");

    return 0;

  }

  if (BN_cmp(dh_pub, BN_value_one()) != 1) { /* pub_exp <= 1 */

    logit("invalid public DH value: <= 1");

    return 0;

  }

  if ((tmp = BN_new()) == NULL) {

    error_f("BN_new failed");

    return 0;

  }

  if (!BN_sub(tmp, dh_p, BN_value_one()) ||

      BN_cmp(dh_pub, tmp) != -1) {   /* pub_exp > p-2 */

    BN_clear_free(tmp);

    logit("invalid public DH value: >= p-1");

    return 0;

  }

  BN_clear_free(tmp);

  for (i = 0; i <= n; i++)

    if (BN_is_bit_set(dh_pub, i))

      bits_set++;

  debug2("bits set: %d/%d", bits_set, BN_num_bits(dh_p));

  /*

   * if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial

   */

  if (bits_set < 4) {

    logit("invalid public DH value (%d/%d)",

        bits_set, BN_num_bits(dh_p));

    return 0;

  }

  return 1;

}

int

dh_gen_key(DH *dh, int need)

{

  int pbits;

  const BIGNUM *dh_p, *pub_key;

  DH_get0_pqg(dh, &dh_p, NULL, NULL);

  if (need < 0 || dh_p == NULL ||

      (pbits = BN_num_bits(dh_p)) <= 0 ||

      need > INT_MAX / 2 || 2 * need > pbits)

    return SSH_ERR_INVALID_ARGUMENT;

  if (need < 256)

    need = 256;

  /*

   * Pollard Rho, Big step/Little Step attacks are O(sqrt(n)),

   * so double requested need here.

   */

  if (!DH_set_length(dh, MINIMUM(need * 2, pbits - 1)))

    return SSH_ERR_LIBCRYPTO_ERROR;

  if (DH_generate_key(dh) == 0)

    return SSH_ERR_LIBCRYPTO_ERROR;

  DH_get0_key(dh, &pub_key, NULL);

  if (!dh_pub_is_valid(dh, pub_key))

    return SSH_ERR_INVALID_FORMAT;

  return 0;

}

DH *

dh_new_group_asc(const char *gen, const char *modulus)

{

  DH *dh;

  BIGNUM *dh_p = NULL, *dh_g = NULL;

  if ((dh = DH_new()) == NULL)

    return NULL;

  if (BN_hex2bn(&dh_p, modulus) == 0 ||

      BN_hex2bn(&dh_g, gen) == 0)

    goto fail;

  if (!DH_set0_pqg(dh, dh_p, NULL, dh_g))

    goto fail;

  return dh;

 fail:

  DH_free(dh);

  BN_clear_free(dh_p);

  BN_clear_free(dh_g);

  return NULL;

}

/*

 * This just returns the group, we still need to generate the exchange

 * value.

 */

DH *

dh_new_group(BIGNUM *gen, BIGNUM *modulus)

{

  DH *dh;

  if ((dh = DH_new()) == NULL)

    return NULL;

  if (!DH_set0_pqg(dh, modulus, NULL, gen)) {

    DH_free(dh);

    return NULL;

  }

  return dh;

}

/* rfc2409 "Second Oakley Group" (1024 bits) */

DH *

dh_new_group1(void)

{

  static char *gen = "2", *group1 =

      "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"

      "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"

      "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"

      "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"

      "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"

      "FFFFFFFF" "FFFFFFFF";

  return (dh_new_group_asc(gen, group1));

}

/* rfc3526 group 14 "2048-bit MODP Group" */

DH *

dh_new_group14(void)

{

  static char *gen = "2", *group14 =

      "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"

      "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"

      "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"

      "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"

      "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE45B3D"

      "C2007CB8" "A163BF05" "98DA4836" "1C55D39A" "69163FA8" "FD24CF5F"

      "83655D23" "DCA3AD96" "1C62F356" "208552BB" "9ED52907" "7096966D"

      "670C354E" "4ABC9804" "F1746C08" "CA18217C" "32905E46" "2E36CE3B"

      "E39E772C" "180E8603" "9B2783A2" "EC07A28F" "B5C55DF0" "6F4C52C9"

      "DE2BCBF6" "95581718" "3995497C" "EA956AE5" "15D22618" "98FA0510"

      "15728E5A" "8AACAA68" "FFFFFFFF" "FFFFFFFF";

  return (dh_new_group_asc(gen, group14));

}

/* rfc3526 group 16 "4096-bit MODP Group" */

DH *

dh_new_group16(void)

{

  static char *gen = "2", *group16 =

      "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"

      "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"

      "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"

      "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"

      "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE45B3D"

      "C2007CB8" "A163BF05" "98DA4836" "1C55D39A" "69163FA8" "FD24CF5F"

      "83655D23" "DCA3AD96" "1C62F356" "208552BB" "9ED52907" "7096966D"

      "670C354E" "4ABC9804" "F1746C08" "CA18217C" "32905E46" "2E36CE3B"

      "E39E772C" "180E8603" "9B2783A2" "EC07A28F" "B5C55DF0" "6F4C52C9"

      "DE2BCBF6" "95581718" "3995497C" "EA956AE5" "15D22618" "98FA0510"

      "15728E5A" "8AAAC42D" "AD33170D" "04507A33" "A85521AB" "DF1CBA64"

      "ECFB8504" "58DBEF0A" "8AEA7157" "5D060C7D" "B3970F85" "A6E1E4C7"

      "ABF5AE8C" "DB0933D7" "1E8C94E0" "4A25619D" "CEE3D226" "1AD2EE6B"

      "F12FFA06" "D98A0864" "D8760273" "3EC86A64" "521F2B18" "177B200C"

      "BBE11757" "7A615D6C" "770988C0" "BAD946E2" "08E24FA0" "74E5AB31"

      "43DB5BFC" "E0FD108E" "4B82D120" "A9210801" "1A723C12" "A787E6D7"

      "88719A10" "BDBA5B26" "99C32718" "6AF4E23C" "1A946834" "B6150BDA"

      "2583E9CA" "2AD44CE8" "DBBBC2DB" "04DE8EF9" "2E8EFC14" "1FBECAA6"

      "287C5947" "4E6BC05D" "99B2964F" "A090C3A2" "233BA186" "515BE7ED"

      "1F612970" "CEE2D7AF" "B81BDD76" "2170481C" "D0069127" "D5B05AA9"

      "93B4EA98" "8D8FDDC1" "86FFB7DC" "90A6C08F" "4DF435C9" "34063199"

      "FFFFFFFF" "FFFFFFFF";

  return (dh_new_group_asc(gen, group16));

}

/* rfc3526 group 18 "8192-bit MODP Group" */

DH *

dh_new_group18(void)

{

  static char *gen = "2", *group18 =

      "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"

      "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"

      "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"

      "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"

      "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE45B3D"

      "C2007CB8" "A163BF05" "98DA4836" "1C55D39A" "69163FA8" "FD24CF5F"

      "83655D23" "DCA3AD96" "1C62F356" "208552BB" "9ED52907" "7096966D"

      "670C354E" "4ABC9804" "F1746C08" "CA18217C" "32905E46" "2E36CE3B"

      "E39E772C" "180E8603" "9B2783A2" "EC07A28F" "B5C55DF0" "6F4C52C9"

      "DE2BCBF6" "95581718" "3995497C" "EA956AE5" "15D22618" "98FA0510"

      "15728E5A" "8AAAC42D" "AD33170D" "04507A33" "A85521AB" "DF1CBA64"

      "ECFB8504" "58DBEF0A" "8AEA7157" "5D060C7D" "B3970F85" "A6E1E4C7"

      "ABF5AE8C" "DB0933D7" "1E8C94E0" "4A25619D" "CEE3D226" "1AD2EE6B"

      "F12FFA06" "D98A0864" "D8760273" "3EC86A64" "521F2B18" "177B200C"

      "BBE11757" "7A615D6C" "770988C0" "BAD946E2" "08E24FA0" "74E5AB31"

      "43DB5BFC" "E0FD108E" "4B82D120" "A9210801" "1A723C12" "A787E6D7"

      "88719A10" "BDBA5B26" "99C32718" "6AF4E23C" "1A946834" "B6150BDA"

      "2583E9CA" "2AD44CE8" "DBBBC2DB" "04DE8EF9" "2E8EFC14" "1FBECAA6"

      "287C5947" "4E6BC05D" "99B2964F" "A090C3A2" "233BA186" "515BE7ED"

      "1F612970" "CEE2D7AF" "B81BDD76" "2170481C" "D0069127" "D5B05AA9"

      "93B4EA98" "8D8FDDC1" "86FFB7DC" "90A6C08F" "4DF435C9" "34028492"

      "36C3FAB4" "D27C7026" "C1D4DCB2" "602646DE" "C9751E76" "3DBA37BD"

      "F8FF9406" "AD9E530E" "E5DB382F" "413001AE" "B06A53ED" "9027D831"

      "179727B0" "865A8918" "DA3EDBEB" "CF9B14ED" "44CE6CBA" "CED4BB1B"

      "DB7F1447" "E6CC254B" "33205151" "2BD7AF42" "6FB8F401" "378CD2BF"

      "5983CA01" "C64B92EC" "F032EA15" "D1721D03" "F482D7CE" "6E74FEF6"

      "D55E702F" "46980C82" "B5A84031" "900B1C9E" "59E7C97F" "BEC7E8F3"

      "23A97A7E" "36CC88BE" "0F1D45B7" "FF585AC5" "4BD407B2" "2B4154AA"

      "CC8F6D7E" "BF48E1D8" "14CC5ED2" "0F8037E0" "A79715EE" "F29BE328"

      "06A1D58B" "B7C5DA76" "F550AA3D" "8A1FBFF0" "EB19CCB1" "A313D55C"

      "DA56C9EC" "2EF29632" "387FE8D7" "6E3C0468" "043E8F66" "3F4860EE"

      "12BF2D5B" "0B7474D6" "E694F91E" "6DBE1159" "74A3926F" "12FEE5E4"

      "38777CB6" "A932DF8C" "D8BEC4D0" "73B931BA" "3BC832B6" "8D9DD300"

      "741FA7BF" "8AFC47ED" "2576F693" "6BA42466" "3AAB639C" "5AE4F568"

      "3423B474" "2BF1C978" "238F16CB" "E39D652D" "E3FDB8BE" "FC848AD9"

      "22222E04" "A4037C07" "13EB57A8" "1A23F0C7" "3473FC64" "6CEA306B"

      "4BCBC886" "2F8385DD" "FA9D4B7F" "A2C087E8" "79683303" "ED5BDD3A"

      "062B3CF5" "B3A278A6" "6D2A13F8" "3F44F82D" "DF310EE0" "74AB6A36"

      "4597E899" "A0255DC1" "64F31CC5" "0846851D" "F9AB4819" "5DED7EA1"

      "B1D510BD" "7EE74D73" "FAF36BC3" "1ECFA268" "359046F4" "EB879F92"

      "4009438B" "481C6CD7" "889A002E" "D5EE382B" "C9190DA6" "FC026E47"

      "9558E447" "5677E9AA" "9E3050E2" "765694DF" "C81F56E8" "80B96E71"

      "60C980DD" "98EDD3DF" "FFFFFFFF" "FFFFFFFF";

  return (dh_new_group_asc(gen, group18));

}

/* Select fallback group used by DH-GEX if moduli file cannot be read. */

DH *

dh_new_group_fallback(int max)

{

  debug3_f("requested max size %d", max);

  if (max < 3072) {

    debug3("using 2k bit group 14");

    return dh_new_group14();

  } else if (max < 6144) {

    debug3("using 4k bit group 16");

    return dh_new_group16();

  }

  debug3("using 8k bit group 18");

  return dh_new_group18();

}

/*

 * Estimates the group order for a Diffie-Hellman group that has an

 * attack complexity approximately the same as O(2**bits).

 * Values from NIST Special Publication 800-57: Recommendation for Key

 * Management Part 1 (rev 3) limited by the recommended maximum value

 * from RFC4419 section 3.

 */

u_int

dh_estimate(int bits)

{

  if (bits <= 112)

    return 2048;

  if (bits <= 128)

    return 3072;

  if (bits <= 192)

    return 7680;

  return 8192;

}

#endif /* WITH_OPENSSL */